proxy: stub the VPC config cache and invalidation code

[knz]

This commit defines cache entries for projects:

• the two "block public or VPC connections" booleans. This is implemented (for now) as a pair of bools because they are always delivered together from the project settings in cplane. The corresponding fields in the /get_endpoint_access_control response are block_public_connections and block_vpc_connections.

  We will use the redis broadcast channel /block_public_or_vpc_access_updated for this. It will be notified when the project settings are changed in the control plane.

• the VPC endpoint ID list. The corresponding field in the /get_endpoint_access_control response is allowed_vpc_endpoint_ids.

  We will use the 2 redis broadcast channels
  /allowed_vpc_endpoint_ids_updated_for_projects and
  /allowed_vpc_endpoint_ids_updated_for_org for this. It will be
  notified when the VPC config service detects a configuration
  change for the project or all projects under an org.

Informs https://github.com/neondatabase/cloud/issues/21426.

[github-actions]

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_{The comment gets automatically updated with the latest test results
2e79c47 at 2024-12-13T09:21:40.544Z :recycle:}